Saint John Climacus (Greek: Ἰωάννης τῆς Κλίμακος; Latin: Ioannes Climacus), also known as John of the Ladder, John Scholasticus and John Sinaites, was a 7th-century Christian monk at the monastery on Mount Sinai. He is revered as a saint by the Roman Catholic, Oriental Orthodox, Eastern Orthodox and Eastern Catholic churches.

There is almost no information about John's life. There is in existence an ancient Vita (life) of the saint by a monk named Daniel of Raithu monastery. Daniel, though claiming to be a contemporary, admits to no knowledge of John's origins—any speculation on John's birth is the result of much later speculation, and is confined to references in the Menologion. The Vitais generally unhelpful for establishing dates of any kind. Formerly scholarship, on the basis of John's entry in the Menologion, had placed him in the latter 6th Century. That view was challenged by J.C. Guy and others, and consensus (such as there is) has shifted to a 7th Century provenance. If Daniel'sVitais trustworthy (and there is nothing against which to judge its accuracy), then John came to theVatosMonastery at Mount Sinai, now Saint Catherine's Monastery, and became a novice when he was about 16 years old. He was taught about the spiritual life by the elder monk Martyrius. After the death of Martyrius, John, wishing to practice greater asceticism, withdrew to a hermitage at the foot of the mountain. In this isolation he lived for some twenty years, constantly studying the lives of the saints and thus becoming one of the most learned Church Fathers. When he was about seventy-five years of age, the monks of Sinai persuaded him to become their Igumen. He acquitted himself of his functions as abbot with the greatest wisdom, and his reputation spread so far that, according to theVita, Pope Gregory the Great wrote to recommend himself to his prayers, and sent him a sum of money for the hospital of Sinai, in which the pilgrims were wont to lodge